This invention relates to a scrubber for efficiently removing dust from an exhaust gas.
In the production of semiconductors and liquid crystal displays (LCD panels), harmful and inflammable gases are used. Such gases may include silane (SiH4) or halogen gases (NF3, CLF3, SF6, CHF3, C2F6, CF4 and the like). Before being exhausted into the atmosphere, such gases must first be made harmless by being treated in an exhaust gas treating system, such as is shown in FIG. 1.
The exhaust gas treating system shown in FIG. 1 comprises an exhaust gas treatment apparatus 1, with an attached scrubber 20. An exhaust gas G containing SiH4 and the like is introduced to a burner 3 of the apparatus 1 in which a flame 4 is generated to heat the gas G and thereby make it innocuous. The resultant gas contains a dust comprised of micro particles in high density, having a size of around 1 xcexcm or less. The gas containing the micro dust particles is then cooled with a coolant 6, such as water, sprayed from a nozzle 5 in a liquid atomizing area 2, and is then introduced into the scrubber 20. The coolant that has been used to cool the gas is discharged through a U-shaped drain pipe 7.
The scrubber 20 comprises a casing 21; an impeller 23 positioned at a central portion of the casing 21, and rotated by a high speed rotation motor 22; and a cylindrical cleaning liquid discharge nozzle 25 positioned at the center of the impeller 23 for spraying a cleaning liquid 24 such as water. Micro dust particles within the exhaust gas are agitated in the rotating impeller 23 together with the cleaning liquid 24 sprayed from the cylindrical cleaning liquid discharge nozzle 25, to be absorbed into the cleaning liquid 24. Cleaning liquid with micro dust particles absorbed therein is discharged through a U-shaped drain pipe 26. The exhaust gas G exiting the impeller is passed through a mist collector 27 and then emitted into the atmosphere through an exhaust gas outlet 28.
However, such a scrubber generally has a low capability of removal of micro-dust, and is able to remove only around 20% to 60% of micro dust particles contained in a gas from the gas.
In accordance with the present invention, there is provided a scrubber comprising: a casing having an exhaust gas inlet and an exhaust gas outlet; an impeller mounted in the casing, and which is rotated about its own axis, an exhaust gas introduced into the center of the impeller through the exhaust gas inlet of the casing; a cleaning liquid supply nozzle positioned at the center of the impeller to spray a cleaning liquid in the impeller; and, a baffle member spaced apart from and surrounding the impeller on which a mixture of the exhaust gas and the cleaning liquid exiting the impeller impinges. In the scrubber, the baffle enhances agitation of the exhaust gas and the cleaning liquid and atomization of the cleaning liquid, whereby dust particles contained in the exhaust gas are efficiently absorbed into the cleaning liquid and thus a rate of removal of the dust particles from the exhaust gas increases.
Specifically, the baffle member comprises a circular plate member spaced apart and surrounding the impeller and a plurality of protrusions provided on and protruding from the circular plate member towards the impeller. The protrusions may be designed to extend in a direction parallel to the axis of the impeller and have a triangular cross section as viewed in a plane perpendicular to the axis of the impeller. The protrusions are spaced apart from each other in a circumferential direction of the circular plate member.
The casing has an upper wall in which the exhaust gas outlet is formed, the impeller is set in the casing such that its axis extends in a horizontal direction. The circular plate of the baffle member is positioned coaxially with the impeller, and is formed to have an exhaust gas exit opening for discharging the exhaust gas outside the circular plate. The exhaust gas exit opening is preferably positioned so that the exhaust gas exiting the exhaust gas exit opening is forced to be turned at an acute angle to move towards the exhaust gas outlet of the casing.
In accordance with an aspect of the present invention, a cylindrical cleaning liquid discharge nozzle is positioned inside and rigidly connected to the impeller and extends in the direction of the axis of the impeller, so that the cylindrical cleaning liquid discharge nozzle is rotated together with the impeller. The cylindrical cleaning liquid discharge nozzle has a cylindrical wall which defines a cylindrical chamber has a plurality of cleaning liquid discharge orifices extending radially through the cylindrical wall. A cleaning liquid supply pipe is fluidly connected to the chamber of the cylindrical cleaning liquid discharge nozzle to supply a cleaning liquid into the chamber. The cleaning liquid is discharged from the rotating cylindrical cleaning liquid discharge nozzle through the orifices to form particles thereof.
Further objects and advantages of the present invention will be apparent from the following description made with reference to the accompanying drawings showing a preferred, embodiment of the present invention.